Vehicle fuel systems include evaporative emission control systems designed to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor canister packed with an adsorbent which adsorbs and stores the vapors. At a later time, when the engine is in operation, the evaporative emission control system allows the vapors to be purged into the engine intake manifold for use as fuel.
Previously disclosed systems place a single fuel tank isolation valve (FTIV) between the fuel tank and the fuel vapor canister. The FTIV may be a solenoid valve under control of a pulse-width modulated signal. The FTIV may be partially opened to regulate fuel tank pressure during engine-on conditions, and fully opened to prepare the fuel tank for refueling.
However, combining tank pressure control with a refueling valve presents numerous potential issues. Opening the FTIV completely when a significant pressure exists within the fuel tank may result in the corking of other fuel tank valves such as a grade vent valve and/or a fill limit vent valve, rendering them unusable. Opening the FTIV in this fashion could also lead to an abundance of hydrocarbons entering the engine intake system, altering the air/fuel ratio, and potentially leading to engine stalling. Additionally, any delays or imprecision in control of an FTIV may increase release of hydrocarbons or degraded air-fuel ratio control during purging.
The inventors herein have recognized the above issues, and have developed systems and methods to at least partially address these issues. In one example, a system for a vehicle, comprising: a tank pressure control valve coupled in a first conduit between a fuel tank and a fuel vapor canister; a refueling valve coupled in a second, different, conduit between the fuel tank and the fuel vapor canister, the second conduit in parallel to the first conduit. In this way, two smaller, less complex valves may be utilized to control fuel tank vapor purging and fuel tank depressurization during refueling. This in turn may lower system cost and increase system functionality.
In another example, a method for a hybrid-electric vehicle, comprising: in response to a refueling request: opening a tank pressure control valve while maintaining a refueling valve closed; allowing a fuel tank pressure to decrease below a first threshold; and opening the refueling valve. In this way, fuel tank depressurization may be controlled during refueling such that fuel tank vent valves are not exposed to rapid pressure changes during refueling events which may cork the valves, rendering them unusable for future fuel tank venting events.
In yet another example, a system for a hybrid-electric vehicle, comprising: a tank pressure control valve coupled in a first conduit between a fuel tank and a fuel vapor canister; a refueling valve coupled in a second conduit between the fuel tank and the fuel vapor canister, the second conduit in parallel to the first conduit; a controller configured with instructions stored in non-transitory memory and executable by a processor to: in response to a refueling request: opening a tank pressure control valve while maintaining a refueling valve closed; allowing a fuel tank pressure to decrease below a first threshold; and opening the refueling valve. In this way, that fuel tank vent valves are not exposed to significant pressure differentials during refueling events which may close the valves, and thus may prevent adequate refueling.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.